Adjustable plug type jet propulsion nozzle



Jan. 28, 1969 H. M. A. R- LAcoMBE 3,424,384

ADJUSTABLE PLUG TYPE JET PROPULSION NOZZLE Filed Sept. 19, 1 966 UnitedStates Patent 3,424,384 ADJUSTABLE PLUG TYPE JET PROPULSION NOZZLE HenryMarie Andr Ren Lacombe, Bois-le-Roi, France, assignor to SocieteNationale dEtude et de Construction de Moteurs dAviation, Paris, France,a company of France Filed Sept. 19, 1966, Ser. No. 580,538 Claimspriority, application France, Sept. 21, 1965,

US. Cl. 239-26539 Int. Cl. B64c 15/06; B05b 1/30 2 Claims ABSTRACT OFTHE DISCLOSURE conjunction with the tapered portion of said tail cone, a

divergent jet pipe section having a mean flow direction which convergeswith respect to the axis of said nozzle.

The present invention relates to jet propulsion nozzles of the so-calledplug type having a tail cone which tapers rearwardly from a part ofmaximum cross-section to a tail end and which forms the inner wall of anannular jet pipe of convergent or convergent-divergent configurationwith its zone of minimum area or throat being at the level of said tailcone part of maximum crosssection.

It has already been proposed to adjust the throat area of such nozzlesby means of flaps extending from an end pivoted on an outer wall at alocation upstream of said part of maximum cross-section to a freetrailing edge positioned opposite said part.

Theoretical studies, which have moreover been corroborated in practice,have revealed two drawbacks of this solution:

(1) The ejection is defective at the level of the flaps. In fact, asthese flaps extend wholly upstream of the above-mentioned part ofmaximum cross-section the mean direction of ejection diverges from thelongitudinal axis of the nozzle. The jet must consequently undergo overthe convex profile of the central body a considerable deflection whichbrings it back towards the axis and which excessively intensifies theeffect of the Prandtl-Meyer expansion originating from the ends of theflaps. Moreover, at certain speeds, the Mach waves, after reflection onthe jet line, form a recompression bundle or beem which focuses in aviolet shock producing losses.

(2) Irnmersing the flaps into the motive gaseous flow creates a dragzone at low pressure behind the flaps and usually secondary air from asurrounding casing is fed into said drag zone to raise the pressurelevel thereof in an attempt to reduce drag losses. However suchsatisfactory operative conditions are not attainable at all flightrunnings for lack of reaching the appropriate pressure level. In fact,if this level is too high, the jet bursts out at a small angle onleaving the flaps and there subsists in the plane of ejection, betweenthe jet boundary line and the end of the casing, a considerable pocketwhich is difficult to ventilate and is always the cause of 3,424,384Patented Jan. 28, 1969 losses. If the level is too low, the jet burstsout very strongly and encounters the casing at a considerable angle, sothat on impact there is created a shock which produces losses and thereis a risk of the hot gases being driven back. This is frequently thecase in highspeed flight.

It is one object of the present invention to provide a jet propulsionnozzle which does not exhibit the faults hereinbefore described.

One embodiment of the invention will now be described by way of examplewith reference to the single figure of the accompanying drawing which isa diagrammatic view in axial half-section of a jet propulsion nozzleembodying the invention.

The nozzle comprises a fixed profiled plug or central body 1 having anupstream portion 2 which is of increasing cross-section in the directionof flow and which is connected, through a part 3 of maximumcross-section, with a downstream portion 4 of decreasing crosssection.The nozzle is defined externally by a fixed wall 5 to which a number ofinner flaps 6 are hinged at a location 7 upstream of part 3; these flapsextend to a free trailing edge positioned downstream of part 3 and sooverride the latter. They cooperate with a number of outer flaps 8 whichare pivoted at 9 at the rear end of a casing having ports 10 for theinlet of ambient air.

In the drawing the lines of the jet boundary are indicated as follows:at A1 and A2 are shown the jet boundary lines corresponding respectivelyto take-off without afterburning (flaps 6 in position 6 and withafterburning (flaps 6 in position 6 the flaps 8 being in position shownin dashes; at B is shown the jet boundary line corresponding totransonic speed (flaps 8 in the position shown in chain-dotted lines);and at C is shown the jet boundary line for supersonic cruising speed(flaps 8 in the position shown in solid lines).

It will be noted that the throat adjusting flaps 6 extend downstream ofpart 3, thus eliminating the drawback mentioned above in respect to theinitial deviation. Moreover, the central body 1 is designed so as toform with these flaps a primary convergent-divergent jet pipe section,the nominal expansion ratio of which at the ends of the flaps alwaysremains close to the minimum expansion ratio of the engine undertake-01f conditions, so that in this case the performances of acorrectly designed and well adapted nozzle can be expected. The jetboundary line A1 or A2 is therefore almost parallel to the downstreamportion 4 of the central body 1.

Whatever the expansion ratio, the terminal flaps 8, which are free orcontrolled, can be directed tangentially to the corresponding jetboundary line, thus preventing inner drag zones of low pressure to buildup in the highvelocity motive jet and transferring them from behind theinner flaps 6 to behind the outer flaps 8 which are bathed in ambientair. This is the case in low-speed flight and in transonic flight(positions shown in dashes and chain-dotted lines, respectively).

At high expansion ratios, the flaps 8, which are in the position ofmaximum opening (solid lines), form with the central body 1 a secondarydivergent structure, the pressures and ventilating flow-rates of whichremain low, in spite of the practicaldisappearance of any inner dragzone. As a matter of fact, the pre-expansion oflered by the inner flaps6 greatly reduces the bursting angle of the jet and still permits thetangential pick-up thereof on the terminal flaps 8.

Whatever the circumstances, the inner flaps 6 are always substantiallyconvergent. Their downstream portion bounds a divergent section adaptedto the expansion ratio.

Moreover, there is generally a slight flow of secondary air induced bythe jet.

What is claimed is:

1. An adjustable jet propulsion nozzle comprising a stationary plugmember which tapers rearwardly from a part thereof of maximumcross-section to a tail end, and movable flaps outwardly spaced withrespect to said plug member and pivoted at a location spaced upstream ofsaid part of maximum cross-section, said flaps ending with a freetrailing edge at a location spaced downstream of said part of maximumcross-section but upstream of said tail end, thereby overriding saidpart of maximum cross-section and defining with said plug member aconvergent-divergent nozzle element with a throat in the zone of saidpart of maximum cross-section, said flaps being adjustably inclinahleinwardly to define, in conjunction with the tapered portion of said plugmember, a divergent nozzle section having a mean flow direction whichconverges with respect to the nozzle axis.

2. Jet propulsion nozzle as claimed in claim 1, further comprising afairing outwardly spaced from said flaps,

and pivotal wall elements'hingedly connected to said fairing and forminga downstream extension thereof, said wall elements extending downstreamof the free trailing edge of said flaps.

References Cited UNITED STATES PATENTS WALTER SOBIN, Primary Examiner.

US. Cl. X.R. 239127.3

